This invention relates to a knock suppression apparatus that suppresses knocking of an internal combustion engine of a vehicle. More particularly, it relates to a knock suppression apparatus that is not adversely affected by electrical noise caused by large currents flowing through the electrical system of the vehicle.
A knock suppression apparatus is a device that detects and suppresses knocking of an internal combustion engine to increase engine efficiency. There are a number of methods that can be used to suppress knocking, but the most commonly-used method is to adjust the ignition timing of the engine. A knock suppression apparatus generally includes a knock sensor in the form of an acceleration sensor that generates an electrical output signal in response to engine vibrations. The output signal of the knock sensor is input to an electronic control unit, which processes the output signal to separate components due to knocking from components due to miscellaneous mechanical vibrations of the engine and electrical noise. Based on the processed signal, the electronic control unit retards the ignition timing until knocking is no longer detected.
The knock sensor is connected with the electronic control unit by wiring that is combined with wiring from other components to form a wiring harness. If the wiring for the knock sensor is in a harness carrying large continuous or large inrush currents, such as the headlight harness, electrical noise will be induced in the wiring for the knock sensor. If the level of the induced electrical noise is high enough, the electronic control unit may mistake the electrical noise for a signal due to engine knocking and retard the ignition timing in response to the noise. If the electronic control unit mistakenly senses knocking and retards the ignition timing when the engine speed is low or decreasing, no significant harm takes place, but if it does so when the vehicle is accelerating, the acceleration of the vehicle will be poor, the fuel consumption will increase, and the driver of the vehicle will receive an unpleasant sensation. In short, the engine efficiency will decrease, and the entire purpose of knock suppression will be defeated.
It is conceivable to electrically isolate the wiring for the knock sensor from other wiring by the use of shielded cable, for example, or to dispose the wiring for the knock sensor so that it is sufficiently remote from other wires to prevent electrical noise from being induced. However, the use of shielded cable increases the cost of a knock suppression apparatus, and in automotive vehicle, where space it is at a premium, it is difficult and inconvenient to physically isolate the wiring for the knock sensor from all other wiring.